Abstract : Alpha-iron is another instance of mimetic twinning in which an edifice formed by a group of twinned tetragonal crystals presents an appearance of cubic symmetry. This confirms earlier suggestions that magnetic domains are crystallographic twins. Crystals of alpha-iron were grown in thin strips of Armco iron, a large magnetic domain size confirmed by examining the Bitter pattern, the crystals examined point by point by means of Laue patterns and an oscillating crystal pattern of a crystal recorded. The Laue patterns confirm the persistence of a single crystal but shifts in relative intensities within the patterns show that clusters of differently oriented twins are illuminated by the x-ray beam at each point. The Laue pattern of a crystal shows a redistribution of relative intensities upon the application of an external magnetic field, indicating a new group of twinned orientations within the region illuminated by the x-ray beam. The pattern from a crystal, supposedly oscillating about a cubic (100) direction, shows layer lines which fit a twin lattice with a triple unit cell and twinned tetragonal crystals oscillating about (110), (001) and (100) directions. (Author)